The primary goal of the proposed research is to understand the molecular genetic basis of the development of B-cell lymphomas in mice. The identification of new loci that are implicated in causing murine B<ell lymphomas will facilitate our understanding of cancer in humans. Retroviruses and other transposable elements are often found as causative agents in murine cancers. Although the role that mobile DNA elements play in disease processes is beginning to be understood, one way these elements can cause cancer is to integrate near, and alter the expression of normal somatic cellular proto-oncogenes. These transposable elements act as insertional mutagens and serve as useful molecular tags to clone new genes associated with tumorigenesis. Some AKXD recombinant inbred strains of mice have a high incidence of B-cell lymphomas caused by the expression and subsequent integration of murine leukemia retroviruses. The B-cell lymphomas in AKXD mice are valuable resources for identifying and cloning new proto-oncogenes associated with lymphoma development using the retrovirus as a molecular tag. A new common site of retroviral integration called ecotropic viral integration site-3 (Evi-3) was molecularly cloned from B-cell lymphomas of the AKXD mice. Bach of the lymphomas with a proviral insertion at Evi- 3 is of B-cell lineage. Two novel genes flank the proviral insertions at Evi-3, and both have properties consistent with their roles as proto- oncogenes. One, Evi-3A, is expressed in mouse embryos, and one, Evi-3B, is expressed in B-cells. The alteration of two genes by a single retroviral integration at Evi-3 provides a paradigm for the multistep nature of the development of cancer. The Evi3 locus in humans maps to human chromosome 18, to a region highly implicated in translocation breakpoints in human synovial sarcoma. Our specific aims are: 1) identify the nature of alterations of the genes caused by the retroviral integrations at Evi-3, 2) show that the normal cellular roles of genes at Evi-3 are consistent with their roles as proto-oncogenes when altered by the retroviral integrations, 3) identify the role of EVI3 in human disease, and 4) obtain additional B-cell lymphomas from the AKXD mice for protein and RNA studies, B-cell differentiation studies, and additional molecular tagging studies. We plan to use molecular and cellular approaches to study gene function. These approaches include additional cloning, sequencing, and gene expression analysis. We also propose to develop additional resources for studying Evi-3 and for cloning new genes associated with other common sites of retroviral integration by aging mice from the AKXD recombinant inbred strains, and preserving tumor cells for expansion. These tumors will be valuable resources for our lab, as well as for other labs studying hematopoietic tumors or B-cell development.